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Abstract

In the face of recent changes in environmental conditions and climate, longterm
studies provide important insights into patterns and processes of vegetational
change. In northern Europe, however, long-term studies are rare
for many ecosystems. This thesis uses a new approach that uses historical
phytosociological data-sets to study changes in the vegetation of alpine,
mire, and arctic habitats and regions across northern Europe over the past
decades. Because plot relocation due to the use of non-permanent plots may
bias the detection of change, the thesis investigates if observed changes are
larger than what is expected by chance. Furthermore, to find out if observed
changes in vegetation are consistent between different habitats and regions
in northern Europe, a meta-analysis of 15 data sets from arctic, alpine, and
mire sites is presented.
The results of the resurvey conducted in alpine Sikkilsdal, Central Norway,
show that most species have shifted their distributional range upwards
along the elevational gradient since the first sampling in the 1920s. These
upward shifts were found to be independent of whether upper, lower, or
optimum elevation were considered. As the largest shifts were found for
species growing in snow-bed habitats, the results suggest climate warming
and alterations in snow-cover duration to be important drivers of the
observed range shifts.
In the Åkhult mire (South Sweden), changes over a period of 54 years
were found predominantly for species of dwarf-shrubs and trees, whereas
several typical mire species have decreased or disappeared from the study
site. Drier mire surface and higher nutrient availability due to a warmer
climate are identified as the most plausible drivers explaining the observed
turnover in species composition.
On Jan Mayen Island, similar changes in vegetation were found during
time periods of 19 and 80 years. Over both time-scales, graminoid and
woody species were found to have increased, whereas several snow-bed
related species have decreased. However, whereas the main trend is similar
over both time-scales considered, discrepancies in the trends of some
species suggest that long-term changes are only partly predictable from
short-term studies. The results of the meta-analysis show that the arrangement between
species has changed more than is expected by chance, indicating that nonrandom
changes have occurred in the studied arctic, alpine, and mire habitats
during the past century. Vegetation stability was found to vary sitespecifically.
Observed patterns could not be explained by different factors,
such as time-scale, plot number, species diversity, or productivity.
The thesis shows that non-random vegetational changes have occurred
independent of which habitat or site is considered. As the observed changes
in vegetation are in line with several other studies on vegetational dynamics
focusing at different temporal and spatial scales and using permanent
plots, this thesis demonstrates that historical phytosociological data-sets
may successfully be used in the way presented here. These results unlock
a valuable archive to identify recent vegetational changes in relation to environmental
change. Moreover, observations of increased growth of woody
plants and graminoids, upward shifts in species ranges, and decreases in
species mostly associated with wetter habitats indicate trends in vegetation
towards more competitive and nutrient-demanding species. With regard
to predicted changes in climate, further changes may be assumed, the effects
of which are likely to be most pronounced in areas where species are
adapted to low temperatures and low nutrient availability, such as in high
mountain areas, raised bogs, and in the Arctic.

Has part(s)

Paper II: Kapfer J., Grytnes J.-A., Gunnarsson U., and Birks H. J. B. (2011) Finescale changes in vegetation composition in a boreal mire over 50 years. Journal of Ecology 99(5): 1179-1189, Mai 2011. Full text not available in BORA due to publisher restrictions. The article is available at: http://dx.doi.org/10.1111/j.1365-2745.2011.01847.x

Paper III: Kapfer J., Virtanen R., and Grytnes J.-A. Changes in arctic vegetation composition on Jan Mayen Island – a comparison of two time scales. Full text not available in BORA.